1. Field of the Invention.
The analysis and study of waveforms often requires a high degree of accuracy. Since such waveforms, including impulses, may exist for very short times, their analysis study may require an ability to retain them for display for indefinite periods. Digital data acquisition apparatus of many descriptions are known which have the requisite accuracy and retention.
2. Description of the Prior Art.
FIGS. 1 and 2 are generalized representations, in schematic form, of digital data acquisition apparatus each of which include an input 10, discriminator 11, clock 12, data collector 13 and output 14. Input 10 is adapted to receive a waveform, including an impulse, and has its output connected to a discriminator 11 and to the data collector 13. The discriminator 11 may include filtering, shaping and similar functions and will typically respond to a waveform parameter to detect the occurrence of an event. The occurrence of the event (trigger event) will result in a trigger signal output from discriminator 11 representative of the occurrence of the trigger event.
In the system illustrated in FIG. 1, the trigger signal output from discriminator 11 is applied as an enable signal to data collector 13 which also receives the waveform to be sampled from input 10 and the output from the system clock 12. In the system illustrated in FIG. 2, a trigger event output from discriminator 11 is connected to the clock 12 to initiate the generation of clock pulses which are provided, as an output from the system clock 12, to the data collector 13, the data collector 13 also receiving the waveform from the input 10. In the systems of both FIGS. 1 and 2, the data collector responds to the output of the clock to periodically sample the waveform from the input 10. The sample rate is based on the clock signal rate. However, the data collector 13 may include dividers, counters, etc. such that the actual rate of data acquisition is proportional to the output rate of the clock 12. Data collector 13 may also include storage for retention of acquired data with the data acquired being provided to an output 14, either directly or from storage. The output 14 may include any desired display or combinations thereof.
One difficulty encountered with the system of the type illustrated in FIG. 1 is the variable interval between the occurrence of a trigger event and the next succeeding, in time, the data acquisition signal from the clock 12. An advantage is that the system of FIG. 1 allows the use of a high quality oscillator for the clock 12 which reduces the variability of the intervals at which sampling of the waveform is performed. In the contrast, the system illustrated in FIG. 2 employs a clock which is triggered by the trigger event, and, by implication, is an oscillator having a relatively low quality factor to provide rapid start up. This low quality factor has an inherent variability in the timing of the sampling of the waveform.